<!DOCTYPE HTML PUBLIC>
<html>
 <head>
  <meta charset="utf-8">
  <title>获取图片像素颜色,转换为css3 box-shadow</title>
  
  <style type="text/css">
    body{margin: 0px; background:#f2f2f0;}
    p{margin:0px;}
    .title{color:#FFFF00; background:#000000; text-align:center; font-size:24px; line-height:50px; font-weight:bold;}
    .file{position:absolute; width:100%; font-size:90px;}
    .filebtn{display:block; position:relative; height:110px; color:#FFFFFF; background:#06980e; font-size:48px; line-height:110px; text-align:center; cursor:pointer; border: 3px solid #cccccc;}
    .filebtn:hover{background:#04bc0d;}
    .showimg{margin:10px auto 10px auto; -webkit-transition: all .3s; transition: all .3s;}
    .showimg span{width:1px; height:1px; display:block; margin: -1px 0px 0px -1px;}
    .css_code{margin:10px; padding:10px; display:none; border:1px solid #FFCC00; font-size:12px; background:#F1F1F1; white-space:pre-wrap; word-wrap:break-word; height:300px; overflow:auto;}
    .css_code:hover{
        background:#DEFEDE;
    }
  </style>
 
  <script type="text/javascript">
  window.onload = function(){
  
    var canvas = document.createElement('canvas');
    var context = canvas.getContext('2d');
    var showimg = document.getElementById('showimg');
    var shadow = showimg.getElementsByTagName('span')[0];
    var css_code = document.getElementById('css_code');
 
    document.getElementById('img').onchange = function(){
        var img = event.target.files[0];
 
        // 检查能否读取图片
        if(!img){
            return ;
        }
 
        // 检查图片类型
        if(!(img.type.indexOf('image')==0 && img.type && /\.(?:jpg|png|gif)$/.test(img.name)) ){
            alert('图片只能是jpg,gif,png');
            return ;
        }
 
        // 检查图片尺寸
        if(img.size > 120*1024){
            alert('图片不能大于120K');
            return ;
        }
 
        // file reader
        var reader = new FileReader();
        reader.readAsDataURL(img);
 
        reader.onload = function(e){ // reader onload start
 
            var image = new Image();
            image.src = e.target.result;
 
            image.onload = function(){ // image onload start
 
                var img_width = this.width;
                var img_height = this.height;
 
                // 设置画布尺寸
                canvas.width = img_width;
                canvas.height = img_height;
 
                // 将图片按像素写入画布
                context.drawImage(this, 0, 0, img_width, img_height);
 
                // 读取图片像素信息
                var imageData = context.getImageData(0, 0, img_width, img_height);
 
                var arrbox = [],
                    length = imageData.data.length;
 
                // 生成box-shadow
                for(var i=0; i<length; i++){
 
                    if(i%4 === 0){ // 每四个元素为一个像素数据 r,g,b,alpha
 
                        var x = i/4%img_width + 1;                               // 横坐标
                        var y = Math.floor(i/4/img_width) + 1;                   // 纵坐标
                        var alpha = Math.round(imageData.data[i+3]/255*100)/100; // alpha 值
 
                        if(imageData.data[i+3]==255){ // 没有alpha 值
                            var hex = gethex(imageData.data[i], imageData.data[i+1], imageData.data[i+2]);
                            arrbox.push(x + 'px ' + y + 'px #' + hex);
                        }else if(alpha>0){ // 有alpha 值
                            var rgba = imageData.data[i] + ',' + imageData.data[i+1] + ',' + imageData.data[i+2] + ',' + alpha;
                            arrbox.push(x + 'px ' + y + 'px rgba(' + rgba + ')');
                        }
 
                    }
                }
 
                // 将数据写入dom
                showimg.style.width = img_width + 'px';
                showimg.style.height = img_height + 'px';
 
                shadow.style.boxShadow = arrbox.join(',');
 
                // 输出CSS3 box-shadow
                css_code.style.display = 'block';
                css_code.innerHTML = 'box-shadow: ' + arrbox.join(',');
 
                
                // 获取16进制颜色
                function gethex(r,g,b){
                    r = r.toString(16);
                    g = g.toString(16);
                    b = b.toString(16);
 
                    // 补0
                    r.length==1? r = '0' + r : '';
                    g.length==1? g = '0' + g : '';
                    b.length==1? b = '0' + b : '';
 
                    var hex = r + g + b;
 
                    // 简化处理,如 FFEEDD 可以写为 FED
                    if(r.slice(0,1)==r.slice(1,1) && g.slice(0,1)==g.slice(1,1) && b.slice(0,1)==b.slice(1,1)){
                        hex = r.slice(0,1) + g.slice(0,1) + b.slice(0,1);
                    }
 
                    return hex;
                }
 
            } // image onload end
        
        } // reader onload end
    }
  
  }
  </script>
 
 </head>
 
 <body>
  <p class="title">获取图片像素颜色,转换为CSS3 box-shadow</p>
  <p><input type="file" class="file" id="img"><label class="filebtn" for="img" title="JPG,GIF,PNG">请选择图片(小于120K)</label></p>
  <p class="showimg" id="showimg"><span></span></p>
  <p class="css_code" id="css_code"></p>
 </body>
</html>
